1. Field
The present disclosure relates to an air pressure control device including a valve seat supported by a diaphragm, and a compression coil spring for biasing the valve seat. The present invention further relates to an adjustment valve equipped with the air pressure control device.
2. Description of the Related Art
As known in the related art, an air pressure apparatus for driving an actuator by air pressure includes an air pressure control device to control an operation of the actuator. That type of air pressure control device has a mechanism of reducing the pressure of air supplied from an air pressure supply source, as disclosed in Japanese Unexamined Utility Model Registration Application Publication No. 7-8604, for example.
A pressure reducing valve 1 illustrated in FIG. 5, for example, is one simplest example of the above-mentioned type of air pressure control device. The pressure reducing valve 1 illustrated in FIG. 5 includes a diaphragm 5 that partitions an inner space of a housing 2 into a first air chamber 3 positioned at the lower side in FIG. 5 and a second air chamber 4 positioned at the upper side. The first air chamber 3 is connected to an air inlet of an actuator (not illustrated). The first air chamber 3 is further connected, through a poppet valve 7, to an upstream-side air chamber 6 positioned at the lowermost side in FIG. 5. The second air chamber 4 is released to the atmosphere through a communication hole (not illustrated).
High-pressure air is supplied to the upstream-side air chamber 6 from an air pressure supply source (not illustrated). The poppet valve 7 includes a communication hole 8 for communicating the first air chamber 3 and the upstream-side air chamber 6 with each other, a valve member 9 for opening or closing an opening of the communication hole 8, the opening being positioned at the upstream side (i.e., at the lower side in FIG. 5), and a spring member 10 for biasing the valve member 9 in a closing direction. The valve member 9 includes a pin 11 projecting into the first air chamber 3 through the communication hole 8.
A valve seat 12 and an area plate 13 are attached to the diaphragm 5. The valve seat 12 penetrates through the diaphragm 5. A through-hole 14 for communicating the first air chamber 3 and the second air chamber 4 with each other is bored in the valve seat 12. The through-hole 14 is positioned coaxially with the pin 11 of the valve member 9. A hole diameter of the through-hole 14 is smaller than an outer diameter of the pin 11. An opening portion of the through-hole 14 at the side facing the pin 11 is formed in a flaring shape with the hole diameter gradually increasing toward an end of the opening portion. A tip end of the pin 11 is inserted into the opening portion of the through-hole 14.
The area plate 13 serves to bear the spring force of a compression coil spring 15, and it is fixed to the valve seat 12 in the second air chamber 4. A plurality of pawls 16 to be held in engagement with an inner peripheral portion of the compression coil spring 15 is vertically disposed on the area plate 13.
The compression coil spring 15 serves to bias the diaphragm 5 toward the first air chamber 3. The compression coil spring 15 is held at one end by the area plate 13 and at the opposite end by an upper seat 17.
The upper seat 17 is formed in a disk-like shape overlapping the opposite end of the compression coil spring 15, and has a recessed portion 17a into which a pointed tip end of a pressure adjusting bolt 18 is inserted. The pressure adjusting bolt 18 is meshed with a housing 2.
The diaphragm 5 of the pressure reducing valve 1 is displaced such that the spring force of the compression coil spring 15 and the pressure in the first air chamber 3 are balanced. When the pressure in the first air chamber 3 decreases from a state in which the spring force of the compression coil spring 15 and the pressure in the first air chamber 3 are balanced, the diaphragm 5 is displaced toward the first air chamber 3 by the spring force of the compression coil spring 15, and the valve seat 12 is pressed against the pin 11 of the valve member 9. At that time, the pin 11 closes the through-hole 14 in the valve seat 12, whereby the communicating state between the first air chamber 3 and the second air chamber 4 is eliminated. When the pin 11 is further pushed by the valve seat 12, the communication hole 8 is opened, thus allowing air to flow into the first air chamber 3 from the upstream-side air chamber 6 through the communication hole 8. The inflow air supplied to the actuator from the first air chamber 3
On the other hand, when the pressure in the first air chamber 3 increases beyond the spring force of the compression coil spring 15, the diaphragm 5 is displaced toward the second air chamber 4, and the valve seat 12 is moved away from the pin 11 of the valve member 9. In that state, the valve member 9 closes the communication hole and the communicating state between the upstream-side air chamber 6 and the first air chamber 3 is eliminated. Furthermore, the air in the first air chamber 3 flows into the second air chamber 4 via the through-hole 14, and is then exhausted to the atmosphere from the second air chamber 4.
The pressure reducing valve 1 constituted as described above has a problem that a center of the through-hole 14 in the valve seat 12 is slightly misaligned from an axis of the pin 11, and a gap is generated between the through-hole 14 and the pin 11 of the valve member 9, thereby causing an exhaust leak (bleeding) in some cases. The exhaust leak becomes a factor of not only making an output pressure unstable, but also bringing about loss of energy. Another problem is that exhaust sounds are noisy.
Moreover, with the occurrence of the exhaust leak, the tip end of the pin 11 of the poppet valve 7 may be forced to repeatedly strike against the valve seat 12 in some cases. In those cases, contact portions of the pin 11 and the valve seat 12 are worn to such an extent that a significant exhaust leak occurs continuously. In addition, when wears of the contact portions of the pin 11 and the valve seat 12 are progressed, the pressure reducing valve may come into a state in which pressure adjustment is failed, thus causing an adjustment valve to malfunction (for example, not to operate or to operate slowly), and giving influences on a variety of apparatuses connected in subsequent stages.
Until now, in order to prevent the above-mentioned exhaust leak, it has been proposed, for example, to increase stability of position of the valve member 9, or to set the pin 11 of the valve member 9 and the through-hole 14 to be positioned coaxially with each other in a manufacturing process. However, because the diaphragm 5 is made of rubber, the position of the valve seat 12 is changed and the center of the through-hole 14 is slightly misaligned from the axis of the pin 11 due to strong influences given by behaviors of the compression coil spring 15 when it is compressed or extended.
When the compression coil spring 15 is compressed, the following three phenomena mainly generate.
In the first phenomenon, an end surface 15a of the compression coil spring 15, which is formed perpendicularly to a center line C of the compression coil spring 15 as illustrated in FIG. 6A, is inclined after the compression as illustrated in FIG. 6B. When the end surface 15a of the compression coil spring 15 is inclined, the area plate 13 and the upper seat 17 are also inclined correspondingly. As a consequence, the position of the valve seat 12 is changed.
In the second phenomenon, as illustrated in FIG. 7 because the area plate 13 and the upper seat 17 are always subjected to vertical spring forces, the magnitudes of the spring forces received by those members become not uniform. In FIG. 7, the magnitudes of the spring forces are indicated by lengths of arrows. Because the magnitudes of the spring forces received by the area plate 13 and the upper seat 17 are not uniform as described above, the area plate 13 and the upper seat 17 are inclined.
In the third phenomenon, because the compression coil spring 15 is compressed from a state illustrated in FIG. 8A to a state illustrated in FIG. 8B, both the ends of the compression coil spring 15 are twisted, this phenomenon being called “twisting”. Torque attributable to the “twisting” is transmitted to the area plate 13 and the upper seat 17, thereby causing torsions and wrinkles of the diaphragm 5. Hence the position of the valve seat 12 is changed.
Because the upper seat 17 is in point contact with the pressure adjusting bolt 18, the upper seat 17 is able to incline or twist together with the end surface 15a of the compression coil spring 15. In contact portions of the upper seat 17 and the pressure adjusting bolt 18, however, a large friction force generates with the contact portions receiving not only frictional resistance caused by the contact, but also a reaction force (spring force) of the compression coil spring 15. This may result in that the upper seat 17 is worn or brought into an eccentric state relative to the pressure adjusting bolt 18, and that the upper seat 17 is hard to slide in some cases. Furthermore, the above-described friction force is greatly changed depending on a position of the pressure adjusting bolt 18 and an amount of compression of the compression coil spring 15, thereby making the contact state of the pressure adjusting bolt 18 unstable and increasing the torque given to the pressure adjusting bolt 18. Thus, a difficulty resides in solving the problems attributable to the above-described three phenomena by utilizing the inclination and rotation of the upper seat 17. In order to solve those problems, it is conceivable to provide, on the area plate 13 and the upper seat 17, guides (not illustrated) for restricting the operating directions of those members. However, using those guides is practically impossible for the reasons of an increase in operating force due to frictional resistances of the guides, wears of the guides, and scoring of sliding portions.